All entry level pre-built track bikes must sacrifice quality in certain areas to get the price low. Like Ira said - entry level bikes are often made from cheaper tubing, skimpier hubs and rims, and so-on. If your Pista/Langster/ect. is your first track bike then you probably won't have an idea of what you really want in a bike until you have a chance to ride the hell out of it.

I recently sold my first off-the-peg track bike and now ride something that I built to my own liking. But I wouldn't have been able to put together the Spicer without knowing what I did/not like about riding. Thats what the first bike helped me figure out.